Thiol-ene inks for 3d printing

ABSTRACT

In one aspect, inks for use with a three-dimensional printing system are described herein. In some embodiments, an ink described herein comprises a thiol monomer component and an ene monomer component. Moreover, in some cases, an ink described herein further comprises an additional (meth)acrylate monomer component differing from the ene monomer component. In some such cases, the additional (meth)acrylate monomer component can be polymerized separately from the thiol and ene monomers of the ink.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 16/410,070, filed May 13, 2019, which is acontinuation of U.S. Non-Provisional patent application Ser. No.15/480,918, filed Apr. 6, 2017; which claims priority pursuant to 35U.S.C. § 119 to U.S. Provisional Patent Application No. 62/319,533,filed on Apr. 7, 2016; each of which is hereby incorporated by referencein its entirety.

FIELD

The present invention relates to inks and, in particular, to inks foruse with three-dimensional (3D) printing systems.

BACKGROUND

Some commercially available 3D printers, such as the Projet™ 3D Printersmanufactured by 3D Systems of Rock Hill, S.C., use inks, which are alsoknown as build materials, that are jetted through a print head as aliquid to form various 3D objects, articles, or parts. Other 3D printingsystems also use an ink that is jetted through a print head or otherwisedispensed onto a substrate. In some instances, the ink is solid atambient temperatures and converts to liquid at elevated jettingtemperatures. In other instances, the ink is liquid at ambienttemperatures. Moreover, in some cases, the ink can be cured followingdispensing and/or deposition of the ink onto the substrate.

Other 3D printers form 3D articles from a reservoir, vat, or containerof a fluid ink or build material or a powdered ink or build material. Insome cases, a binder material or a laser, digital light processing (DLP)source, or other source of energy is used to selectively solidify orconsolidate layers of the ink or build material in a stepwise orlayer-by-layer fashion to provide the 3D article.

Inks for 3D printing systems can be used to form a variety of articlesfor a variety of applications, including in a manner describedhereinabove. However, some inks for 3D printing systems include(meth)acrylates as a primary curable material. Such inks may providehigh printing resolution but may also provide printed 3D articles thatare rigid and brittle or flexible but easily broken. Therefore, thereexists a need for improved inks for 3D printing, including inks that canprovide a combination of desirable properties, such as high printingresolution and high toughness.

SUMMARY

In one aspect, inks for use with a 3D printer are described hereinwhich, in some embodiments, may offer one or more advantages over priorinks. In some embodiments, for example, an ink described herein can beused to form printed 3D articles having high toughness and highresolution, as well as other desirable mechanical properties.

In some embodiments, an ink for use in a 3D printing system describedherein comprises a thiol monomer component and an ethylenicallyunsaturated monomer component. The thiol monomeric component cancomprise one or more than one thiol-containing chemical species.Similarly, the ethylenically unsaturated monomer component can compriseone or more ethylenically unsaturated chemical species. The thiolmonomer component and the ethylenically unsaturated monomer componentcan be chosen to react with one another in a so-called thiol-enereaction. Thus, the ethylenically unsaturated monomer component of anink described herein can also be referred to as an “ene” monomercomponent.

Moreover, in some cases, an ink described herein further comprises anadditional (meth)acrylate monomer component differing from the enemonomer component. In some such instances, the additional (meth)acrylatemonomer component can be polymerized separately from the thiol and enemonomers of the ink. For example, in some instances, the thiol and enemonomers of the ink can react with one another to form a first polymernetwork through a thiol-ene reaction, and the additional (meth)acrylatemonomer of the ink can react with itself to form a second polymernetwork. In such cases, the first and second polymer networks can beseparate or differing polymer networks. Additionally, in someembodiments, the first and second polymer networks together form aninterpenetrating polymer network. Moreover, the first and second polymernetworks can be formed through differing polymerization processes.

It is also possible, in some embodiments, for the additional(meth)acrylate monomer of the ink to react with itself and also with theene monomer of the ink. In such an instance, only one polymer networkmay be formed. Additionally, in some embodiments, an ink comprises athiol monomer and an ene monomer, and the ene monomer is present in astoichiometric excess compared to the thiol monomer. In some such cases,the ene monomer may react with the thiol monomer to provide a firstpolymer network (specifically, a thiol-ene polymer network) and mayfurther react with itself to provide a second polymer network (such as aseparate poly(meth)acrylate network). Thus, in some such instances,interpenetrating polymer networks may be provided without the use of anadditional (meth)acrylate monomer that differs from the ene monomer.

An ink described herein might be particularly useful for a 3D printingsystem, such as a contacting stereolithography (cSLA) printing system orother stereolithography (SLA) printing system, in which the thiolmonomer, the ene monomer, and, optionally, the additional (meth)acrylatemonomer are combined under conditions (e.g., time, temperature, and/orpolymerization inhibitor conditions) that are not sufficient forsubstantial thiol-ene reaction between the thiol monomer and the enemonomer (or additional (meth)acrylate monomer) to occur prior toprinting.

Alternatively, as described further hereinbelow, 3D printing may becarried out using a plurality of inks, wherein a first ink comprises athiol monomer, and a second ink comprises an ene monomer. The second inkmay also optionally include an additional (meth)acrylate monomerdiffering from the ene monomer. Such a dual ink system may beparticularly useful for a 3D printing system, such as a multi-jetmodeling (MjM) system, in which it may not be desirable to combine thethiol monomer with the ene monomer (or with the additional(meth)acrylate monomer) prior to printing. (However, it is to beunderstood that a “single” ink may also be used in an MjM system,provided that conditions disfavoring premature reaction of the inkcomponents (such as conditions provided by a strong polymerizationinhibitor) are present.) Thus, in another aspect, kits for use in a 3Dprinting system are described herein. In some embodiments, such a kitcomprises a first ink comprising a thiol monomer component and a secondink comprising an ene monomer component.

It is to be understood that inks described herein, whether “single” inksor inks that are part of a kit, may further comprise one or moreadditional components in addition to monomers described hereinabove. Forexample, in some embodiments, an ink described herein further comprisesone or more additives selected from the group consisting of colorants,inhibitors, stabilizing agents, photoinitiators, and photosensitizers.

In another aspect, uses of a composition for 3D printing are describedherein, wherein the composition comprises an ink or kit describedhereinabove. For instance, in some cases, a use of a composition for 3Dprinting is described herein, wherein the composition comprises a thiolmonomer and an ene monomer.

In still another aspect, 3D printing systems are described herein. Sucha 3D printing system can comprise a composition for 3D printingdescribed hereinabove, such as a composition comprising an ink or kitdescribed hereinabove. In some embodiments, a 3D printing systemdescribed herein comprises a 3D printer having at least one inkdispenser or ink reservoir, and a composition described herein disposedin the ink dispenser or the ink reservoir. The composition can compriseany ink described herein for use in 3D printing. For example, in somecases, a 3D printing system described herein comprises a 3D printerhaving at least one of an ink dispenser and an ink reservoir, and an inkdisposed in the ink dispenser, the ink reservoir, or both, wherein theink comprises a thiol monomer. Moreover, in some instances, such a 3Dprinter further comprises a second ink dispenser or reservoir and asecond ink disposed in the second ink dispenser or reservoir, whereinthe second ink comprises an ene monomer.

In another aspect, methods of printing a 3D article are describedherein, wherein the method is carried out using one or more inksdescribed herein. In some cases, such a method comprises selectivelyjetting or otherwise depositing layers of an ink in a fluid state onto asubstrate, wherein the ink comprises a thiol monomer and an ene monomercomponent. Additionally, in some cases, the layers of the ink aredeposited in a layer-by-layer manner according to an image of the 3Darticle in a computer readable format. Moreover, in some embodiments, amethod described herein further comprises polymerizing or curing thethiol monomer and the ene monomer. Such curing may be carried out in alayer-by-layer manner during the printing process, or in a“post-processing” step, such as a curing step carried out aftercompletion of printing of all layers of the article. Further, wheneverin the process it occurs, such curing can comprise reacting the thiolmonomer with the ene monomer to form a thiol-ene polymerization reactionproduct, which may also be referred to as a “poly(thiol-ene)” or as a“thiol-ene polymer or oligomer.”

Moreover, in some instances, an ink used in a method described hereincomprises an additional (meth)acrylate monomer that differs from the enemonomer that participates in thiol-ene polymerization. In such cases,the method can further comprise curing the additional (meth)acrylatemonomer with electromagnetic radiation, such as ultraviolet (UV) lightor visible light. Such curing can comprise polymerizing theethylenically unsaturated moieties of the (meth)acrylate monomer to forma poly(meth)acrylate. Additionally, in some cases, as described furtherherein, the poly(meth)acrylate and the poly(thiol-ene) can together forman interpenetrating polymer network.

A method of printing a 3D article described herein can be carried outusing a plurality of inks rather than one ink described herein. Such amethod, in some cases, comprises selectively depositing layers of afirst ink in a fluid state onto a substrate, and selectively depositinglayers of a second ink in a fluid state onto the substrate, wherein thefirst ink and the second ink comprise a first ink and a second ink,respectively, of a kit described herein. In particular, the first inkcan comprise a thiol monomer, and the second ink can comprise an enemonomer. In addition, in some embodiments, the first ink and/or thesecond ink further comprises an additional (meth)acrylate monomer thatdiffers from the ene monomer of the second ink. In some such instances,the method further comprises photocuring the additional (meth)acrylatemonomer, such as with UV light. Such curing can comprise polymerizingthe ethylenically unsaturated moieties of the additional (meth)acrylatemonomer to form a poly(meth)acrylate. A method described herein mayfurther comprise curing the thiol monomer of the first ink and the enemonomer of the second ink, which may comprise reacting the thiol monomerwith the ene monomer to form a poly(thiol-ene). A poly(meth)acrylate andpoly(thiol-ene) formed from a plurality of inks in this manner cantogether form an interpenetrating polymer network.

Further, in still other embodiments, a method of printing a 3D articledescribed herein does not necessarily comprise jetting or otherwisedepositing one or more inks described herein onto a substrate accordingto digital data representing the 3D article. Instead, in some cases, amethod of printing a 3D article described herein comprises retaining anink in a fluid state in a container, and selectively applying energy tothe ink in the container to solidify at least a portion of a first fluidlayer of the ink, thereby forming a first solidified layer that definesa first cross-section of the article. The ink can comprise any inkdescribed hereinabove. Moreover, such a method can further compriseraising or lowering the first solidified layer to provide a second fluidlayer of the ink at a surface of the fluid ink in the container, andselectively applying energy to the ink in the container to solidify atleast a portion of the second fluid layer of the ink, thereby forming asecond solidified layer that defines a second cross-section of thearticle. The first cross-section and the second cross-section are bondedto one another in a z-direction.

In another aspect, printed 3D articles are described herein. Sucharticles can be formed from one or more inks and/or using one or moremethods described hereinabove.

These and other embodiments are described in greater detail in thedetailed description which follows.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by referenceto the following detailed description and examples. Elements, apparatusand methods described herein, however, are not limited to the specificembodiments presented in the detailed description and examples. Itshould be recognized that these embodiments are merely illustrative ofthe principles of the present disclosure. Numerous modifications andadaptations will be readily apparent to those of skill in the artwithout departing from the spirit and scope of the disclosure.

In addition, all ranges disclosed herein are to be understood toencompass any and all subranges subsumed therein. For example, a statedrange of “1.0 to 10.0” should be considered to include any and allsubranges beginning with a minimum value of 1.0 or more and ending witha maximum value of 10.0 or less, e.g., 1.0 to 5.3, or 4.7 to 10.0, or3.6 to 7.9.

All ranges disclosed herein are also to be considered to include the endpoints of the range, unless expressly stated otherwise. For example, arange of “between 5 and 10” or “from 5 to 10” should generally beconsidered to include the end points 5 and 10.

Further, when the phrase “up to” is used in connection with an amount orquantity, it is to be understood that the amount is at least adetectable amount or quantity. For example, a material present in anamount “up to” a specified amount can be present from a detectableamount and up to and including the specified amount.

The terms “three-dimensional printing system,” “three-dimensionalprinter,” “printing,” and the like generally describe various solidfreeform fabrication techniques for making three-dimensional articles orobjects by stereolithography, selective deposition, jetting, fuseddeposition modeling, multi-jet modeling, and other additivemanufacturing techniques now known in the art or that may be known inthe future that use a build material or ink to fabricatethree-dimensional objects.

I. Inks and Kits for 3D Printing

In one aspect, inks for use with a 3D printer are described herein. Insome embodiments, an ink described herein comprises a thiol monomer andan ene monomer. Further, in some instances, an ink described herein alsocomprises an additional (meth)acrylate monomer that differs from the enemonomer. Moreover, an ink described herein, in some cases, furthercomprises a colorant, such as a molecular dye, a particulate inorganicpigment, or a particulate organic colorant. An ink described herein mayalso comprise one or more additives selected from the group consistingof inhibitors, stabilizing agents, photoinitiators, andphotosensitizers.

Turning now in detail to specific components of inks, an ink describedherein comprises a thiol monomer. It is to be understood that a thiol“monomer,” for reference purposes herein, is not limited to a specificmolecular weight or to a specific chemical structure. Instead, a thiol“monomer” can be any thiol-containing chemical species that can reactwith an ethylenically unsaturated chemical species in a thiol-enereaction, such as a thiol-ene polymerization reaction, in which a thiol(S—H) moiety is added across a carbon-carbon double bond of an ene toform a new carbon-sulfur covalent bond and a new carbon-hydrogencovalent bond. Moreover, a thiol “monomer” can comprise a plurality ofthiol moieties. For example, in some instances, a thiol monomercomprises two, three, or four thiol moieties.

Any thiol monomer not inconsistent with the objectives of the presentdisclosure may be used in an ink described herein. For instance, in someembodiments, a thiol monomer comprises an alkyl thiol, a thiol glycolateester, or a thiol propionate ester. Moreover, in some instances, such analkyl thiol, thiol glycolate ester, or thiol propionate ester comprisesa plurality of thiol moieties, including at differing terminuses of themonomer.

In some cases, a thiol monomer comprises a chemical species having thestructure of Formula (A1), (A2), (A3), (A4), or (A5):

wherein R₁, R₂, R₃, and R₄ are each independently a linear or branchedC1-C36 alkyl or alkylene, alkenyl or alkenylene, aryl or arylene, orheteroaryl or heteroarylene moiety; R₅, R₆, R₇, and R₈ are eachindependently H or CH₃; a, b, c, and d are each independently an integerfrom 1 to 100; and m is an integer from 1 to 36. For example, in somecases, one or more of R₁, R₂, R₃, and R₄ is CH₂ or CH₂CH₂; and R₅, R₆,R₇, and R₈ are each H.

Non-limiting examples of thiol monomers suitable for use in someembodiments described herein include pentaerythritoltetra(3-mercaptopropionate) (PETMP) (commercially available from BRUNOBROCK under the trade name THIOCURE PETMP, PETMP I.o., or PETMP sl),trimethylol-propane tri(3-mercaptopropionate) (TMPMP) (commerciallyavailable from BRUNO BOCK), glycol di(3-mercaptopropionate) (GDMP)(commercially available from BRUNO BOCK), pentaerythritoltetramercaptoacetate (PETMA) (commercially available from BRUNO BOCK),trimethylol-propane trimercaptoacetate (TMPMA) (commercially availablefrom BRUNO BOCK), glycol dimercaptoacetate (GDMA) (commerciallyavailable from BRUNO BOCK), ethoxylated trimethylolpropanetri(3-mercaptopropionate) (ETTMP) (commercially available from BRUNOBOCK under the trade name ETTMP 700 or ETTMP 1300, depending onmolecular weight), propyleneglycol 3-mercaptopropionate (PPGMP)(commercially available from BRUNO BOCK under the trade name PPGMP 800or PPGMP 2200, depending on molecular weight),tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate (TEMPIC) (commerciallyavailable from BRUNO BOCK), polycaprolactone tetra 3-mercaptopropionate(commercially available from BRUNO BOCK under the trade name PCL4MP1350), 2,3-di((2-mercaptoethyl)thio)-1-propane-thiol (DMPT)(commercially available from BRUNO BOCK), dimercaptodiethylsulfide(DMDS) (commercially available from BRUNO BOCK), pentaerythritoltetrakis(3-mercaptobutylate) (commercially available from SHOWA DENKOunder the trade name KARENZ MT PEI), 1,4-bis (3-mercaptobutylyloxy)butane (commercially available from SHOWA DENKO under the trade nameKARENZ MT BD1), and1,3,5-tris(3-mercaptobutyloxethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione(commercially available from SHOWA DENKO under the trade name KARENZ MTNR1). Other thiol monomers may also be used in an ink described herein.

It is further to be understood that a thiol monomer component of an inkdescribed herein can comprise only one chemical species or a pluralityof differing chemical species. For example, in some cases, the thiolmonomer of an ink described herein comprises a plurality of differingthiol-containing species. Any combination of differing thiol-containingspecies not inconsistent with the objectives of the present disclosuremay be used in an ink described herein.

Moreover, the thiol monomer component, in total, can be present in anink in any amount not inconsistent with the objectives of the presentdisclosure. For example, in some cases, an ink described hereincomprises up to 50 wt. %, up to 40 wt. %, up to 30 wt. %, up to 25 wt.%, or up to 20 wt. thiol monomer, based on the total weight of the ink.In some instances, an ink comprises 5-50 wt. %, 5-40 wt. %, 10-50 wt. %,10-40 wt. %, 10-30 wt. %, 10-20 wt. %, 15-50 wt. %, 15-40 wt. %, 15-30wt. %, or 15-25 wt. % thiol monomer, based on the total weight of theink.

Inks described herein also comprise an ene monomer. It is to beunderstood that an ene “monomer” is not limited to a specific molecularweight or chemical structure. Instead, an ene “monomer” can comprise anychemical species comprising one or more ethylenically unsaturatedmoieties that can react with a thiol monomer in a thiol-ene reaction toform a sulfur-carbon covalent bond.

Any ene monomer not inconsistent with the objectives of the presentdisclosure may be used in an ink described herein. In some cases, an enemonomer comprises a vinyl moiety, allyl moiety, propenyl moiety, and/or(meth)acrylate moiety, where the term “(meth)acrylate” includes acrylateor methacrylate or a mixture or combination thereof. Further, an enemonomer described herein can be a monofunctional, difunctional,trifunctional, tetrafunctional, pentafunctional, or higher functionalmonomer. A “monofunctional” monomer, for reference purposes herein,comprises a chemical species that includes one ethylenically unsaturatedmoiety. Similarly, a “difunctional” monomer comprises a chemical speciesthat includes two ethylenically unsaturated moieties; a “trifunctional”monomer comprises a chemical species that includes three ethylenicallyunsaturated moieties; a “tetrafunctional” monomer comprises a chemicalspecies that includes four ethylenically unsaturated moieties; and a“pentafunctional” monomer comprises a chemical species that includesfive ethylenically unsaturated. Thus, in some embodiments, amonofunctional ene monomer of an ink described herein comprises amono(meth)acrylate, a difunctional ene monomer of an ink describedherein comprises a di(meth)acrylate, a trifunctional ene monomer of anink described herein comprises a tri(meth)acrylate, a tetrafunctionalene monomer of an ink described herein comprises a tetra(meth)acrylate,and a pentafunctional ene monomer of an ink described herein comprises apenta(meth)acrylate. Other monofunctional, difunctional, trifunctional,tetrafunctional, and pentafunctional ene monomers may also be used. Insome cases, difunctional or higher functional ene monomers areespecially preferred.

Moreover, a monofunctional, difunctional, trifunctional,tetrafunctional, and pentafunctional monomer, in some cases, cancomprise a relatively low molecular weight species or a relatively highmolecular weight species. For example, a monomer can comprise or beeither a “monomeric” or molecular species (i.e., a species that isitself not a polymer or oligomer, that is a relatively low molecularweight species, or that is a relatively low viscosity species), or an“oligomeric” species (i.e., a species that is itself a polymer oroligomer, that is a relatively high molecular weight species, or that isa relatively high viscosity species) that is capable of undergoingadditional polymerization, such as through one or more points ofunsaturation described herein. Thus, in some cases, a population of“monomeric” or molecular species in a monomer can have a consistent orwell-defined molecular structure and/or formula throughout thepopulation (such as may be exhibited, for instance, by a specified massof ethoxylated (4) bisphenol A diacrylate). In contrast, a population of“oligomeric” species in a monomer can have a varying molecular structureand/or formula throughout the population (such as may be exhibited, forexample, by a specified mass of a urethane acrylate having a non-unitymolecular weight distribution, or by a specified mass of an ethoxylatedpolyethylene glycol having a distribution of ethylene glycol unitsand/or a distribution of ethoxy units within the population). Further,the weight average molecular weight of an “oligomeric” monomer cangenerally be in the range from about 400 to 10,000, from about 600 to10,000, or from about 500 to 7,000. The molecular weight of a“monomeric” monomer, in contrast, can generally be below 600, below 500,below 400, below 300, below 200, or below 100. Additionally, in someembodiments, a “monomeric” monomer has a viscosity of 500 centipoise(cP) or less at 25° C., when measured according to ASTM D2983, while an“oligomeric” monomer has a viscosity of 1000 cP or more at 25° C., whenmeasured according to ASTM D2983.

In general, any monomeric ene monomer not inconsistent with theobjectives of the present disclosure may be used in an ink describedherein. In some cases, the ene monomer comprises one or more species of(meth)acrylates, such as one or more monofunctional, difunctional,trifunctional, tetrafunctional (meth)acrylates, and/or pentafunctional(meth)acrylates. In some embodiments, for instance, a monomeric enemonomer comprises methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate,n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate, 2-methoxyethyl(meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2- or 3-ethoxypropyl(meth)acrylate, tetrahydrofurfuryl methacrylate, isobornyl(meth)acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, cyclohexylmethacrylate, 2-phenoxyethyl acrylate, glycidyl acrylate, isodecylacrylate, 2-phenoxyethyl (meth)acrylate, lauryl methacrylate, or acombination thereof. In some embodiments, a monomeric ene monomercomprises one or more of allyl acrylate, allyl methacrylate, triethyleneglycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, andcyclohexane dimethanol diacrylate. Additionally, in some cases, amonomeric ene monomer comprises diacrylate and/or dimethacrylate estersof aliphatic, cycloaliphatic or aromatic diols, including 1,3- or1,4-butanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol,triethylene glycol, tetraethylene glycol, tripropylene glycol,1,4-dihydroxymethylcyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane orbis(4-hydroxycyclohexyl)methane, hydroquinone, 4,4′-dihydroxybiphenyl,bisphenol A, bisphenol F, or bisphenol S. An ene monomer describedherein may also comprise 1,1-trimethylolpropane tri(meth)acrylate,pentaerythritol monohydroxy tri(meth)acrylate, dipentaerythritolmonohydroxy penta(meth)acrylate, and/or bis(trimethylolpropane)tetra(meth)acrylate. Further, in some cases, an ene monomer can comprisean ethoxylated or propoxylated species, such as ethoxylated orpropoxylated neopentyl glycol, ethoxylated or propoxylated bisphenol A,ethoxylated or propoxylated bisphenol F, ethoxylated or propoxylatedbisphenol S, ethoxylated or propoxylated1,1,1-trimethylolpropanetri(meth)acrylate, or ethoxylated orpropoxylated glycerol tri(meth)acrylate.

Additional non-limiting examples of commercially available monomeric enemonomers useful in some embodiments described herein include thefollowing: isobornyl acrylate (IBOA), commercially available fromSARTOMER under the trade name SR 506; isobornyl methacrylate,commercially available from SARTOMER under the trade name SR 423A;triethylene glycol diacrylate, commercially available from SARTOMERunder the trade name SR 272; triethylene glycol dimethacrylate,commercially available from SARTOMER under the trade name SR 205;tricyclodecane dimethanol diacrylate, commercially available fromSARTOMER under the trade name SR 833S; tris(2-hydroxy ethyl)isocyanuratetriacrylate, commercially available from SARTOMER under the trade nameSR 368; 2-phenoxyethyl acrylate, commercially available from SARTOMERunder the trade name SR 339; ethyoxylated (3 mole) bisphenol Adiacrylate, commercially available from SARTOMER under the trade name SR349; and dipentaerythritol pentaacrylate, commercially available fromSARTOMER under the trade name SR 399 LV. Other commercially availablemonomeric ene monomers may also be used.

In addition, any oligomeric ene monomer not inconsistent with theobjectives of the present disclosure may be used in an ink describedherein. In some cases, for instance, the ene monomer comprises apolyester (meth)acrylate oligomer, a urethane (meth)acrylate oligomer,or an epoxy(meth)acrylate oligomer. Further, in some embodiments, anoligomeric ene monomer described herein comprises an aliphatic polyesterurethane acrylate oligomer and/or an acrylate amine oligomeric resin,such as EBECRYL 7100. In some cases, an oligomeric ene monomer describedherein comprises a polypropylene glycol mono(meth)acrylate orpolyethylene glycol mono(meth)acrylate. In some embodiments, anoligomeric ene monomer comprises a monofunctional aliphatic urethane(meth)acrylate. Moreover, in some cases, an oligomeric ene monomercomprises a diacrylate and/or dimethacrylate ester of an aliphatic,cycloaliphatic or aromatic diol, including polyethylene glycol,ethoxylated or propoxylated neopentyl glycol, ethoxylated orpropoxylated bisphenol A, ethoxylated or propoxylated bisphenol F,ethoxylated or propoxylated bisphenol S, ethoxylated or propoxylated1,1,1-trimethylolpropanetri(meth)acrylate, or ethoxylated orpropoxylated glycerol tri(meth)acrylate.

Some non-limiting examples of commercially available oligomeric enemonomers useful in some embodiments described herein include thefollowing: alkoxylated tetrahydrofurfuryl acrylate, commerciallyavailable from SARTOMER under the trade name SR 611; monofunctionalurethane acrylate, commercially available from RAHN USA under the tradename GENOMER 1122; and aliphatic urethane diacrylate, commerciallyavailable from ALLNEX under the trade name EBECRYL 8402. Othercommercially available oligomeric ene monomers may also be used.

Urethane (meth)acrylates suitable for use in inks described herein, insome cases, can be prepared in a known manner, typically by reacting ahydroxyl-terminated urethane with acrylic acid or methacrylic acid togive the corresponding urethane (meth)acrylate, or by reacting anisocyanate-terminated prepolymer with hydroxyalkyl acrylates ormethacrylates to give the urethane (meth)acrylate. Suitable processesare disclosed, inter alia, in EP-A 114 982 and EP-A 133 908. The weightaverage molecular weight of such (meth)acrylate oligomers, in somecases, can be from about 400 to 10,000 or from about 500 to 7,000.Urethane (meth)acrylates are also commercially available from SARTOMERunder the product names CN980, CN981, CN975 and CN2901, or from BOMARSpecialties Co. under the product name BR-741. In some embodimentsdescribed herein, a urethane (meth)acrylate oligomer has a viscosityranging from about 140,000 centipoise (cP) to about 160,000 cP at about50° C. or from about 125,000 cP to about 175,000 cP at about 50° C. whenmeasured in a manner consistent with ASTM D2983. In some cases, aurethane (meth)acrylate oligomer has a viscosity ranging from about100,000 cP to about 200,000 cP at about 50° C. or from about 10,000 cPto about 300,000 cP at about 50° C. when measured in a manner consistentwith ASTM D2983.

It is to be understood that the ene monomer of an ink described hereincan comprise only one chemical species or a plurality of differingchemical species. For example, in some cases, the ene monomer of an inkdescribed herein comprises a plurality of differing ethylenicallyunsaturated species, such as one or more differing monomeric(meth)acrylates and/or one or more differing oligomeric (meth)acrylates.It is further to be understood that, when both an oligomeric species anda monomeric species are included in an ene monomer of an ink describedherein, the ratio of oligomeric species to monomeric species in the inkcan be selected to provide an ink having a viscosity suitable for use ina desired 3D printing system, such as a 3D printing system using apiezoelectric print head to dispense inks, or a stereolithography 3Dprinting system.

Many of the foregoing examples of ene monomers described herein are(meth)acrylates. In some embodiments, the use of such (meth)acrylatesmay be advantageous for some 3D printing applications. However, it isalso possible for the ene monomer to be or comprise a chemical speciesother than a (meth)acrylate. Moreover, in some embodiments, the enemonomer of an ink described excludes (meth)acrylates or is substantiallyfree of (meth)acrylates. An ene monomer that is “substantially” free of(meth)acrylates, for reference purposes herein, can include less than 10wt. %, less than 5 wt. %, less than 3 wt. %, or less than 1 wt. %(meth)acrylates, based on the total weight of the ene monomer.

In some embodiments, an ene monomer comprises a substituted orunsubstituted norbornene, vinyl ether, alkene, vinyl ester, N-vinylamide, allyl ether, allyl triazine, allyl isocyanurate, maleimide (suchas an N-substituted maleimide), acrylonitrile, styrene, conjugateddiene, or a combination thereof. Other non-(meth)acrylate ene monomersmay also be used.

An ene monomer can be present in an ink described herein in any amountnot inconsistent with the objectives of the present disclosure. In somecases, the ene monomer, in total, is present in an amount up to about 90wt. %, up to about 80 wt. %, up to about 70 wt. %, up to about 60 wt. %,up to about 50 wt. %, up to about 40 wt. %, up to about 30 wt. %, or upto about 20 wt. %, based on the total weight of the ink. In some cases,an ink described herein comprises about 10-90 wt. %, 10-80 wt. %, 10-70wt. %, 20-90 wt. %, 20-85 wt. %, 20-75 wt. %, 20-70 wt. %, 20-60 wt. %,20-50 wt. %, 30-80 wt. %, 30-70 wt. %, 40-80 wt. %, 40-70 wt. %, 50-90wt. %, 50-80 wt. %, or 50-70 wt. % ene monomer, based on the totalweight of the ink.

Inks described herein, in some embodiments, also comprise an additional(meth)acrylate monomer component differing from the ene monomercomponent of the ink. It may be particularly desirable to use such anadditional (meth)acrylate monomer in embodiments in which the enemonomer is free or substantially free of (meth)acrylates. As describedabove, in some such cases, the additional (meth)acrylate monomer can bepolymerized or cured separately from the thiol and ene monomers of theink. For example, in some instances, the thiol and ethylenicallyunsaturated monomers of the ink can react with one another to form afirst polymer network through a thiol-ene polymerization reaction, andthe additional (meth)acrylate monomers of the ink can react with oneanother to form a second polymer network. In such cases, the first andsecond polymer networks can be separate or differing polymer networksformed by separate or differing polymerization processes. Additionally,in some embodiments, the first and second polymer networks can togetherform an interpenetrating polymer network.

The use of two differing polymerization processes (such as a thiol-enepolymerization process and a separate (meth)acrylate polymerizationprocess) can permit a printed 3D article formed from a thiol monomer, anene monomer, and an additional (meth)acrylate monomer described hereinto be cured in stages, rather than being cured in a unitary fashion.Moreover, differing stages of curing can be temporally separated fromone another and/or spatially separated from one another within thegeometry of the 3D article. For example, in some embodiments, a firstmonomer (or pair of monomers, such as a pair of thiol and ene monomers)can be cured during printing of the 3D article to provide a printedarticle having sufficient green strength to be handled and/or to exhibita desired feature resolution, and a second monomer (or pair of monomers)can be cured following printing, such as by placing the article in anoven for thermal curing of the second monomer (“printing” in thiscontext is to be understood to include the process of forming theprinted article by providing successive layers or cross-sections of thearticle, and to exclude any “post-printing” or “post-processing” stepssuch as infiltration of the printed article with an infiltrant orheating of the printed article). In other cases, the first monomer (orpair of monomers) cures or polymerizes within a first region of theprinted 3D article, and the second monomer (or pair of monomers) curesor polymerizes within a second region of the printed 3D article, whereinthe first and second regions are different regions.

Additionally, dual polymerization or curing may also be provided,including in a temporally or spatially segregated manner, without theuse of an additional (meth)acrylate monomer that differs from the enemonomer. For instance, in some embodiments, an ink comprises a thiolmonomer and an ene monomer, and the ene monomer is present in astoichiometric excess compared to the thiol monomer. In some such cases,the ene monomer may react with the thiol monomer to provide a firstpolymer network (specifically, a thiol-ene polymer network) and mayfurther react with itself to provide a second polymer network (such as aseparate poly(meth)acrylate network).

Any additional (meth)acrylate monomer not inconsistent with theobjectives of the present disclosure may be used in an ink describedherein. In general, any (meth)acrylate species or combination of(meth)acrylate species described hereinabove in the context of the enemonomer may also be used as the additional (meth)acrylate monomer of anink described herein. It is further to be understood that the additional(meth)acrylate monomer of an ink described herein can comprise only one(meth)acrylate species or a plurality of differing (meth)acrylatespecies. For example, in some embodiments, the additional (meth)acrylatemonomer of an ink described herein comprises a monomeric (meth)acrylatedescribed hereinabove and an oligomeric (meth)acrylate describedhereinabove.

An additional (meth)acrylate monomer can be present in an ink describedherein in any amount not inconsistent with the objectives of the presentdisclosure. In some cases, the additional (meth)acrylate monomer, intotal, is present in an amount up to about 80 wt. %, up to about 70 wt.%, up to about 60 wt. %, up to about 50 wt. %, up to about 40 wt. %, upto about 30 wt. %, up to about 20 wt. %, or up to about 10 wt. %, basedon the total weight of the ink. In some cases, an ink described hereincomprises about 5-80 wt. %, 10-70 wt. %, 10-60 wt. %, 15-80 wt. %, 20-75wt. %, 20-65 wt. %, 20-50 wt. %, 20-40 wt. %, 30-70 wt. %, 30-60 wt. %,40-70 wt. %, 40-60 wt. %, 50-80 wt. %, or 50-70 wt. % additional(meth)acrylate monomer, based on the total weight of the ink.

Inks described herein can further comprise one or more components inaddition to the monomers described hereinabove. For instance, an inkdescribed herein can further comprise a colorant, such as a moleculardye, a particulate inorganic pigment, or a particulate organic colorant.An ink described herein may also comprise one or more additives selectedfrom the group consisting of inhibitors and stabilizing agents. Further,an ink described herein can include one or more photoinitiators and/orone or more photosensitizers.

An ink can comprise any colorant not inconsistent with the objectives ofthe present disclosure. The colorant of an ink described herein can be aparticulate colorant, such as a particulate pigment, or a molecularcolorant, such as a molecular dye. Any such particulate or molecularcolorant not inconsistent with the objectives of the present disclosuremay be used. In some cases, for instance, the colorant of an inkcomprises an inorganic pigment, such as TiO₂ and/or ZnO. In someembodiments, the colorant of an ink comprises a colorant for use in aRGB, sRGB, CMY, CMYK, L*a*b*, or Pantone® colorization scheme. In someinstances, one or more colorants of an ink described herein exhibits awhite color. In other cases, a colorant exhibits a black color. Somenon-limiting examples of colorants suitable for use in some embodimentsdescribed herein include SUN UVDJ107, SUN UVDJ150, SUN UVDJ322, SUNUVDJ350, SUN UVDJ354, RJA D3010-FX-Y150, RJA D3410-FX-Y150, RJAD3410-FX-K, PENN COLOR 9B898, and PENN COLOR 9B989. Moreover, in somecases, a particulate colorant described herein has an average particlesize of less than about 5 μm, or less than about 1 μm. In someinstances, a particulate colorant described herein has an averageparticle size of less than about 500 nm, such as an average particlesize of less than about 400 nm, less than about 300 nm, less than about250 nm, less than about 200 nm, or less than about 150 nm. In someinstances, a particulate colorant has an average particle size of about50-5000 nm, about 50-1000 nm, or about 50-500 nm.

A colorant can be present in an ink described herein in any amount notinconsistent with the objectives of the present disclosure. In somecases, colorant is present in the ink in an amount up to about 2 wt. %,or an amount of about 0.005-2 wt. %, 0.01-2 wt. %, 0.01-1.5 wt. %,0.01-1 wt. %, 0.01-0.5 wt. %, 0.1-2 wt. %, 0.1-1 wt. %, 0.1-0.5 wt. %,or 0.5-1.5 wt. %, based on the total weight of the ink.

Moreover, inks described herein, in some embodiments, further compriseone or more polymerization inhibitors and/or stabilizing agents. Apolymerization inhibitor can be added to an ink to provide additionalthermal stability to the composition. Any polymerization inhibitor notinconsistent with the objectives of the present disclosure may be used.Moreover, a polymerization inhibitor can retard or decrease the rate ofpolymerization, and/or prevent polymerization from occurring for someperiod of time or “induction time” until the polymerization inhibitor isconsumed. Further, in some cases, a polymerization inhibitor describedherein is an “addition type” inhibitor. An inhibitor described hereincan also be a “chain transfer type” inhibitor. In some instances, asuitable polymerization inhibitor comprises methoxyhydroquinone (MEHQ).

A stabilizing agent, in some embodiments, comprises one or moreanti-oxidants. A stabilizing agent can comprise any anti-oxidant notinconsistent with the objectives of the present disclosure. In somecases, suitable anti-oxidants include various aryl compounds, includingbutylated hydroxytoluene (BHT), which can also be used as apolymerization inhibitor in some embodiments described herein. Moregenerally, a single species may serve as both a stabilizing agent and apolymerization inhibitor. It is also possible, in some cases, to use aplurality of inhibitors and/or stabilizing agents, wherein differinginhibitors and/or stabilizers provide differing effects and/or worksynergistically.

A polymerization inhibitor and/or a stabilizing agent can be present inan ink in any amount not inconsistent with the objectives of the presentdisclosure. In some embodiments, a polymerization inhibitor is presentin an amount ranging from about 0.01 wt. % to about 2 wt. % or fromabout 0.05 wt. % to about 1 wt. %. Similarly, in some cases, astabilizing agent is present in an ink in an amount ranging from about0.1 wt. % to about 5 wt. %, from about 0.5 wt. % to about 4 wt. %, fromabout 0.5 wt. % to about 1.5 wt. %, or from about 1 wt. % to about 3 wt.%, based on the total weight of the ink.

An ink described herein may also comprise one or more photoinitiators.Any photoinitiator not inconsistent with the objectives of the presentdisclosure may be used. In some cases, a photoinitiator comprises analpha-cleavage type (unimolecular decomposition process) photoinitiatoror a hydrogen abstraction photosensitizer-tertiary amine synergist,operable to absorb light between about 250 nm and about 400 nm orbetween about 300 nm and about 385 nm, to yield free radical(s).Examples of alpha cleavage photoinitiators are Irgacure 184 (CAS947-19-3), Irgacure 369 (CAS 119313-12-1), and Irgacure 819 (CAS162881-26-7). An example of a photosensitizer-amine combination isDarocur BP (CAS 119-61-9) with diethylaminoethylmethacrylate.

In addition, in some instances, photoinitiators comprise benzoins,including benzoin, benzoin ethers, such as benzoin methyl ether, benzoinethyl ether and benzoin isopropyl ether, benzoin phenyl ether andbenzoin acetate, acetophenones, including acetophenone,2,2-dimethoxyacetophenone and 1,1-dichloroacetophenone, benzil, benzilketals, such as benzil dimethyl ketal and benzil diethyl ketal,anthraquinones, including 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone and2-amylanthraquinone, triphenylphosphine, benzoylphosphine oxides, suchas 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO),benzophenones, such as benzophenone and4,4′-bis(N,N′-dimethylamino)benzophenone, thioxanthones and xanthones,acridine derivatives, phenazine derivatives, quinoxaline derivatives or1-phenyl-1,2-propanedione, 2-O-benzoyl oxime, 1-aminophenyl ketones or1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,phenyl 1-hydroxyisopropyl ketone and 4-isopropylphenyl1-hydroxyisopropyl ketone.

Photoinitiators can also comprise photoinitiators operable for use witha HeCd laser radiation source, including acetophenones,2,2-dialkoxybenzophenones and 1-hydroxyphenyl ketones, such as1-hydroxycyclohexyl phenyl ketone or 2-hydroxyisopropyl phenyl ketone(=2-hydroxy-2,2-dimethylacetophenone). Additionally, in some cases,photoinitiators comprise photoinitiators operable for use with an Arlaser radiation source including benzil ketals, such as benzil dimethylketal. In some embodiments, a photoinitiator comprises anα-hydroxyphenyl ketone, benzil dimethyl ketal or2,4,6-trimethylbenzoyldiphenylphosphine oxide or a mixture thereof.

Another class of photoinitiator that may be included in an ink describedherein comprises ionic dye-counter ion compounds capable of absorbingactinic radiation and generating free radicals for polymerizationinitiation. Some ionic dye-counter ion compounds and their mode ofoperation are disclosed in EP-A-0 223 587 and U.S. Pat. Nos. 4,751,102;4,772,530; and 4,772,541.

A photoinitiator can be present in an ink described herein in any amountnot inconsistent with the objectives of the present disclosure. In someembodiments, a photoinitiator is present in an ink in an amount of up toabout 5 wt. %, based on the total weight of the ink. In some cases, aphotoinitiator is present in an amount ranging from about 0.1 wt. % toabout 5 wt. %.

Additionally, in some embodiments, an ink described herein furthercomprises one or more photosensitizers. In general, such a sensitizercan be added to an ink to increase the effectiveness of one or morephotoinitiators that may also be present. In some cases, a sensitizercomprises isopropylthioxanthone (ITX) or 2-chlorothioxanthone (CTX).

A sensitizer can be present in an ink in any amount not inconsistentwith the objectives of the present disclosure. In some embodiments, asensitizer is present in an amount ranging from about 0.1 wt. % to about2 wt. % or from about 0.5 wt. % to about 1 wt. %, based on the totalweight of the ink.

Some non-limiting examples of inks according to the present disclosureare provided in Table I and Table II below. Specifically, Table I andTable II each provide weight percents for various components ofexemplary inks, where the weight percents are based on the total weightof the ink. In Table I, the heading “Thiol” refers to thiol monomer,“Ene” refers to ene monomer, “AMM” refers to additional (meth)acrylatemonomer, “PI” refers to photoinitiator, “Stab.” refers to stabilizingagent, and “Colorant” refers to colorant. In Table II, “Mono.” refers tomonomeric (meth)acrylate, and “Olig.” refers to oligomeric(meth)acrylate.

TABLE I Ink Components. Ink Thiol Ene AMM PI Stab. Colorant 1  5-40 5-40 15-60 0.5-2.5 0.2-2   0-2 2  5-30  5-30 35-60 1-2 0.2-1.5 0-2 3 5-20  5-20 55-70 0.5-3   0.2-1   0.1-1   4 10-40 10-40 15-70 1-50.5-2.5 0.1-0.5 5 10-30 10-30 35-70 0.1-3   0.5-5   0.1-1.5 6 15-2515-25 45-70 0.1-2   1-5 0.005-2   

TABLE II Ink Components. Ink Thiol Mono. Olig. PI Stab. Colorant  7 5-40 10-60  5-60 0.5-2.5 0.2-2   0.01-2    8  5-40 10-50 10-50 1-40.1-1   0-2  9 15-25 20-50 10-50 0.5-3   0.2-1   0.1-1   10 15-25 20-5010-50 1-5 0.5-2.5 0.1-0.5

As described hereinabove, 3D printing may be carried out according tothe present disclosure using a single ink capable of forming a polymeror oligomer from a thiol monomer, an ene monomer, and, optionally, anadditional (meth)acrylate monomer. However, it is also possible to carryout 3D printing using a combination of differing inks that, whencombined, are capable of forming a polymer or oligomer from a thiolmonomer, an ene monomer, and, optionally, an additional (meth)acrylatemonomer. Thus, in another aspect, kits for use in a 3D printing systemare described herein. In some embodiments, such a kit comprises a firstink comprising a thiol monomer and a second ink comprising an enemonomer. Moreover, in some cases, the first ink and/or the second inkfurther comprises an additional (meth)acrylate monomer. The first inkand/or the second ink may also comprise a photoinitiator, inhibitor,stabilizing agent, and/or colorant.

Further, it is to be understood that the thiol monomer, ene monomer,additional (meth)acrylate monomer, photoinitiator, inhibitor,stabilizing agent, and colorant of a kit described herein can compriseany thiol monomer, ene monomer, additional (meth)acrylate monomer,photoinitiator, inhibitor, stabilizing agent, and colorant describedherein for a “single” ink. Additionally, it is further to be understoodthat the first or second ink of a kit described herein can include aplurality or mixture of thiol species, a plurality or mixture ofethylenically unsaturated species, a plurality or mixture of additional(meth)acrylate species, a plurality or mixture of photoinitiators, aplurality or mixture of inhibitors, a plurality or mixture ofstabilizing agents, and/or a plurality or mixture of colorants. Ingeneral, any combination or mixture of differing thiol species,ethylenically unsaturated species, additional (meth)acrylate species,photoinitiators, inhibitors, stabilizing agents, and/or colorantsdescribed herein may be used in a first ink and/or a second ink of a kitdescribed herein. However, in some cases, an ink of a kit describedherein does not comprise both a thiol species and also an ethylenicallyunsaturated species such as a (meth)acrylate.

Moreover, the inks of a kit described herein may be used simultaneouslyor sequentially in a 3D printing process. Additionally, in some cases,the inks of the kit can together provide differing monomers or curablematerials that form differing polymer networks. In some such instances,the differing monomers and/or polymer networks of the differing inks ofa kit can be cured in a temporally separated manner and/or a spatiallyseparated manner within the geometry of the 3D article, as describedabove for single inks. For example, in some embodiments, a monomer (orpair of monomers) of the first (and/or second) ink can be cured duringprinting of the 3D article to provide a printed article havingsufficient green strength to be handled and/or to exhibit a desiredfeature resolution, and a different monomer (or pair of monomers) of thesecond (and/or first) ink can be cured following printing, such as byplacing the article in an oven for thermal curing of the second monomer.Similarly, in other cases, a monomer (or pair of monomers) of the firstink cures or polymerizes within a first region of the printed 3Darticle, and a monomer (or pair of monomers) of the second ink cures orpolymerizes within a second region of the printed 3D article.

In addition, the two inks of a kit described herein can be used inseparate ink dispensers or “channels” of a 3D printing system during 3Dprinting, or may be combined to form a single composition for forming a3D article, as described further hereinbelow. Further, it is to beunderstood that a “channel” of a 3D printing system can refer to amechanism for depositing a single material from an ink dispenser such asa print head. For example, a channel of a print head can refer to aspecific material ejection orifice of a print head, alone or incombination with any material conduits, material storage compartments,and/or other hardware or software of a 3D printing system associatedwith the specific material ejection orifice. A channel can also refer toan entire print head dedicated to printing a single, specific material,alone or in combination with any material conduits, material storagecompartments, and/or other hardware or software of a 3D printing systemassociated with printing the single, specific material from the channel.

Inks described herein, whether “single” inks or part of a kit, canexhibit a variety of desirable properties. For example, an ink describedherein can have any freezing point, melting point, and/or other phasetransition temperature not inconsistent with the objectives of thepresent disclosure. In some cases, an ink has freezing and meltingpoints consistent with temperatures used in some 3D printing systems,including 3D printing systems designed for use with phase changing inks.In some embodiments, the freezing point of an ink is greater than about40° C. In some instances, for example, an ink has a freezing pointcentered at a temperature ranging from about 45° C. to about 55° C. orfrom about 50° C. to about 80° C. In some cases, an ink has a freezingpoint below about 40° C. or below about 30° C.

Further, in some embodiments described herein, an ink exhibits a sharpfreezing point or other phase transition. In some cases, for instance,an ink freezes over a narrow range of temperatures, such as a range ofabout 1-10° C., about 1-8° C., or about 1-5° C. In some embodiments, anink having a sharp freezing point freezes over a temperature range ofX±2.5° C., where X is the temperature at which the freezing point iscentered (e.g., X=65° C.).

In addition, an ink described herein, in some cases, is fluid at jettingtemperatures encountered in some 3D printing systems. Moreover, in someembodiments, an ink solidifies once deposited on a surface during thefabrication of a three-dimensionally printed article or object.Alternatively, in other instances, an ink remains substantially fluidupon deposition on a surface. Solidification of an ink, in someembodiments, occurs through a phase change of the ink or a component ofthe ink. The phase change can comprise a liquid to solid phase change ora liquid to semi-solid phase change. Further, in some instances,solidification of an ink comprises an increase in viscosity of the ink,such as an increase in viscosity from a low viscosity state to a highviscosity state. Solidification of an ink can also occur due to curingof the ink.

Additionally, in some embodiments, an ink described herein, whennon-cured, has a viscosity profile consistent with the requirements andparameters of one or more 3D printing systems, such as a multi-jetmodeling or stereolithography system. In some cases, for example, an inkdescribed herein has a dynamic viscosity ranging from about 8.0 cP toabout 14.0 cP or from about 9.0 to about 14.0 cP at a jettingtemperature of the system, such as a temperature of about 80° C., whenmeasured according to ASTM standard D2983 (e.g., using a BrookfieldModel DV-II+ Viscometer). In some embodiments, an ink has a dynamicviscosity of about 9.5-12.5 cP or about 10.5-12.5 cP at a temperature ofabout 80° C. In some cases, an ink has a viscosity of about 8.0-10.0 cPat a temperature of about 85-87° C. In some embodiments, an inkdescribed herein has a dynamic viscosity of about 8.0-19.0 cP, about8.0-13.5 cP, about 11.0-14.0 cP, about 11.5-13.5 cP, or about 12.0-13.0cP at a temperature of about 65° C., when measured according to ASTMD2983. In other instances, an ink described herein when non-curedexhibits a dynamic viscosity of about 200-2000 cP, about 200-900 cP,about 300-900 cP, about 300-800 cP, about 400-1000 cP, about 400-900 cP,about 400-800 cP, about 400-600 cP, about 450-550 cP, about 500-700 cP,about 500-600 cP, or about 500-550 cP at 30° C., when measured accordingto ASTM D2983. In some cases, an ink described herein when non-curedexhibits a dynamic viscosity of less than about 100 cP or more thanabout 1000 cP, when measured according to ASTM D2983.

Further, inks described herein, in some embodiments, can exhibit acombination of one or more desirable features. In some cases, forinstance, an ink in the non-cured state has one or more of the followingproperties:

1. Freezing point below about 30° C., below about 25° C., or below about15° C.;

2. Viscosity of about 9-14 cP at 70-95° C. or about 400-1000 cP at25-35° C.; and

3. Thermal stability for at least 6 months at room temperature (25° C.).

As described above, viscosity can be measured according to ASTM D2983(e.g., using a Brookfield Model DV-II+ Viscometer). In addition, forreference purposes herein, a “thermally stable” material exhibits nogreater than about a 35 percent change in viscosity over a specifiedtime period (e.g., 3 days) when measured at the specified temperature(e.g., room temperature) at the beginning and at the end of the timeperiod. In some embodiments, the viscosity change is no greater thanabout 30 percent or no greater than about 20 percent, based on thelarger viscosity value. In some cases, the viscosity change is betweenabout 10 percent and about 20 percent or between about 25 percent andabout 30 percent. Moreover, in some embodiments, the change in viscosityis an increase in viscosity.

Inks described herein can also exhibit a variety of desirableproperties, in addition to those described hereinabove in a cured stateor in a “green” state. An ink in a “cured” state, as used herein,comprises an ink that includes a curable material or polymerizablecomponent that has been at least partially polymerized and/orcross-linked or that has been largely polymerized and/or cross-linked.For instance, in some cases, a cured ink is at least about 51%polymerized or cross-linked or at least about 60% polymerized orcross-linked. In some embodiments, a cured ink is at least about 70%, atleast about 80%, at least about 90%, or at least about 95% polymerizedor cross-linked. In some instances, a cured ink is between about 50% andabout 99% polymerized or cross-linked. An ink in a “green” state can beless than 50%, less than 40%, less than 30%, or less than 20%polymerized or cross-linked. In some cases, an ink in a green state is5-50%, 5-40%, 5-30%, 10-50%, 10-40%, 10-30%, 20-50%, 20-40%, 30-50%, or30-40% polymerized or cross-linked. Moreover, as understood by one ofordinary skill in the art, a “green” state of an ink can be defined asthe state of the ink during or after a layer-by-layer 3D printingprocess described herein but before a post-processing curing step hasbeen performed.

In some cases, an ink described herein, when cured or in a green state,has an elongation at break of about 10-400%, 10-300%, 10-200%, 10-100%,10-8-%, 10-40%, 10-30%, 10-20%, 15-400%, 15-300%, 15-100%, 15-30%,50-400%, 50-300%, 50-200%, 50-100%, 100-400%, 100-300%, 100-200%,200-400, 200-300%, or 300-400%, when measured according to ASTM D638.Further, a cured or green ink described herein, in some cases, can havea tensile strength of about 3500-7000 psi or about 4000-6000 psi, whenmeasured according to ASTM D638. Additionally, a cured or green inkdescribed herein, in some embodiments, can have a tensile modulus ofabout 100-400 ksi or about 150-300 ksi, when measured according to ASTMD638.

Moreover, in some cases, an ink described herein, when cured, canexhibit a plurality of the foregoing properties. For example, in someembodiments, an ink when cured has a tensile strength of about 4000-6000psi when measured according to ASTM D638; a tensile modulus of about150-300 ksi when measured according to ASTM D638; and an elongation atbreak of about 10-400% when measured according to ASTM D638.

Inks described herein can be produced in any manner not inconsistentwith the objectives of the present disclosure. In some embodiments, forinstance, a method for the preparation of an ink described hereincomprises the steps of mixing the components of the ink, melting themixture, and filtering the molten mixture. Melting the mixture, in somecases, is carried out at a temperature of about 75° C. or in a rangefrom about 75° C. to about 85° C. In some embodiments, an ink describedherein is produced by placing all components of the ink in a reactionvessel and heating the resulting mixture to a temperature ranging fromabout 75° C. to about 85° C. with stirring. The heating and stirring arecontinued until the mixture attains a substantially homogenized moltenstate. In general, the molten mixture can be filtered while in aflowable state to remove any large undesirable particles that mayinterfere with jetting or extrusion or other printing process. Thefiltered mixture can then be cooled to ambient temperatures and storeduntil ready for use in a 3D printing system. In other instances, thecomponents of an ink are mixed at ambient temperature (e.g., 20-25° C.),without heating, or with minimal heating (e.g., to a temperature of30-45° C.). Such a method can still include filtering the resultingliquid mixture.

II. Uses of Compositions for 3D Printing

In another aspect, uses of a composition for 3D printing are describedherein, wherein the composition comprises an ink or kit describedhereinabove. For instance, in some cases, a use of a composition for 3Dprinting is described herein, wherein the composition comprises an inkcomprising a thiol monomer and an ene monomer. However, any ink orplurality of inks described hereinabove in Section I may be used for 3Dprinting.

III. 3D Printing Systems

In still another aspect, 3D printing systems are described herein. Sucha 3D printing system can use or comprise a composition for 3D printingdescribed hereinabove, such as a composition comprising an ink,plurality of inks, or kit described hereinabove. In some embodiments, a3D printing system described herein comprises a 3D printer having atleast one of an ink dispenser and an ink reservoir, and an ink describedherein disposed in the ink dispenser, the ink reservoir, or both. Theink comprises, consists of, or consists essentially of any ink describedhereinabove in Section I. Additionally, in some cases, a 3D printingsystem described herein comprises a 3D printer having a first inkdispenser and a second ink dispenser, a first ink disposed in the firstink dispenser, and a second ink disposed in the second ink dispenser.The first ink and the second ink each comprise, consist of, or consistessentially of a first ink and a second ink described hereinabove inSection I.

In general, any 3D printer not inconsistent with the objectives of thepresent disclosure may contain or include an ink described herein,including in an ink dispenser and/or reservoir. In some embodiments, forexample, the 3D printer comprises an inkjet or so-called multi-jetmodeling (MjM) type 3D printer. In other instances, the 3D printercomprises a stereolithography (SLA) type 3D printer, a digital lightprocessing (DLP) type 3D printer, or a contacted SLA (cSLA) typeprinter. Other 3D printers may also be used.

IV. Methods of Printing a 3D Article

In another aspect, methods of printing a 3D article or object aredescribed herein. Methods of printing a 3D article or object describedherein can include forming the 3D article from a plurality of layers ofan ink described herein in a layer-by-layer manner. Any ink describedhereinabove in Section I may be used. For example, in some cases, theink comprises a thiol monomer and an ene monomer. Other inks describedherein may also be used. Moreover, in some cases, a method describedherein comprises selectively depositing layers of the ink in a fluidstate onto a substrate.

Additionally, a method described herein can further comprise curing orpolymerizing one or more monomers or curable materials of the ink, suchas the thiol monomer and the ene monomer of the ink. Moreover, when anink comprises a plurality of monomers having differing polymerizationprocesses or curing mechanisms, the differing monomers can be cured orpolymerized in separate curing or polymerization steps carried out atdifferent time periods and/or in different spatial regions of a layer ofink. Further, differing monomers can be cured or polymerized indifferent manners.

For instance, in some cases, an ink used in a method described hereincomprises a thiol monomer, an ene monomer, and an additional(meth)acrylate monomer differing from the ene monomer. In some suchinstances, a method described herein comprises curing or polymerizingthe ethylenically unsaturated moieties of the (meth)acrylate monomer toform a poly(meth)acrylate. For example, the (meth)acrylate monomer canbe cured or polymerized with UV light. Further, in some embodiments, themethod further comprises separately curing or polymerizing the thiolmonomer and the ene monomer. Such curing or polymerizing can comprisereacting the thiol monomer with the ene monomer to form apoly(thiol-ene). Moreover, reaction of the thiol monomer with the enemonomer, in some cases, is thermally initiated. In other embodiments,reaction of the thiol monomer with the ene monomer is photoinitiated.However, in some such cases, photocuring the additional (meth)acrylatemonomer is carried out using a different wavelength or intensity oflight, compared to photocuring the thiol monomer and the ene monomer. Itis also possible to initiate reaction of the thiol monomer with the enemonomer using the same light used to initiate polymerization of theadditional (meth)acrylate monomer. Additionally, in some instances,thermal energy released by the photoinitiated polymerization of the(meth)acrylate monomer is used to initiate reaction of the thiol monomerwith the ene monomer.

Curing or polymerizing one or more curable materials or monomersdescribed herein can be carried out in any manner not inconsistent withthe objectives of the present disclosure. For example, in someinstances, a layer of deposited ink can be polymerized or cured prior tothe deposition of another or adjacent layer of ink. Thus, in some cases,a method of printing a 3D article described herein further comprisesexposing a layer of ink to electromagnetic radiation of sufficientwavelength and intensity to cure at least one monomer (or pair ofmonomers) of the ink, where curing can comprise polymerizing one or morepolymerizable moieties or functional groups of one or more components ofthe monomer (or pair of monomers). In some embodiments, UV light orvisible light is used.

Similarly, curing can also be carried out thermally. In someembodiments, as described above, thermal curing is carried out usingthermal energy or heat provided by a photocuring step described herein,including thermal energy released by the photoinitiated polymerizationof a (meth)acrylate monomer. Thermal curing can also be carried out byheating the ink (or an article formed from the ink) using a source ofthermal energy such as an oven. Thermal curing may be carried out duringlayer-by-layer printing, or after layer-by-layer printing of thearticle. For example, in some cases, an article is heated in a“post-processing” step, such as by placing the previously formed articlein an oven or other space at an elevated temperature. In some suchinstances, the article can be heated at a temperature and for a timeperiod sufficient to cure a previously uncured monomer of an ink fromwhich the article is formed, as opposed to being heated at a lowertemperature and/or for a shorter time period, such as may be used tomelt a support material off or away from a completed 3D article.However, in some instances, a support material, if present, may bemelted off a completed 3D article at the same time as thermal curing ofa monomer of the ink.

As described above, a method of printing a 3D article described hereincan comprise forming the 3D article from a plurality of layers of aplurality of inks described herein in a layer-by-layer manner, ratherthan from a single ink. For instance, in some embodiments, a methodcomprises forming the 3D article from a plurality of layers of a firstink and a plurality of layers of a second ink. In some such cases, amethod of printing a 3D article comprises selectively depositing layersof a first ink in a fluid state onto a substrate and selectivelydepositing layers of a second ink in a fluid state onto the substrate,wherein the first ink and the second ink respectively comprise a firstink and a second ink described hereinabove in Section I. For example,the first ink can comprise a thiol monomer and the second ink cancomprise an ene monomer.

As with “single” inks, methods described herein using a plurality ofdiffering inks can also comprise curing a plurality of monomers orcurable materials of the inks, including in separate curing stepscarried out at different time periods and/or in different spatialregions of a layer of one or more inks. Moreover, as described furtherherein, different monomers or curable materials can be cured indifferent manners. For example, in some embodiments, the second inkcomprises an additional (meth)acrylate monomer, and the method furthercomprises curing the additional (meth)acrylate monomer of the second inkwith UV light and subsequently thermally curing or photocuring the thiolmonomer and the ene monomer.

In general, the layers of an ink or plurality of inks can be depositedaccording to an image of the 3D article in a computer readable format.In some embodiments, an ink is deposited according to preselectedcomputer aided design (CAD) parameters. Moreover, in some cases, one ormore layers of an ink described herein has a thickness of about 10 μm toabout 100 μm, about 10 μm to about 80 μm, about 10 μm to about 50 μm,about 20 μm to about 100 μm, about 20 μm to about 80 μm, or about 20 μmto about 40 μm. Other thicknesses are also possible.

Additionally, it is to be understood that methods of printing a 3Darticle described herein can include so-called multi-jet modeling orstereolithography 3D printing methods. For example, in some instances, amulti-jet method of printing a 3D article comprises selectivelydepositing layers of one or more inks described herein in a fluid stateonto a substrate, such as a build pad of a 3D printing system. Inaddition, in some embodiments, a method described herein furthercomprises supporting at least one of the layers of the one or more inkswith a support material. Any support material not inconsistent with theobjectives of the present disclosure may be used.

Further, in some embodiments, a preselected amount of ink describedherein is heated to the appropriate temperature and jetted through theprint head or a plurality of print heads of a suitable inkjet printer toform a layer on a print pad in a print chamber. In some cases, eachlayer of ink is deposited according to the preselected CAD parameters. Asuitable print head to deposit the ink, in some embodiments, is apiezoelectric print head. Additional suitable print heads for thedeposition of ink and support material described herein are commerciallyavailable from a variety of ink jet printing apparatus manufacturers.For example, Xerox, Hewlett Packard, or Ricoh print heads may be used insome instances.

Additionally, in some embodiments, an ink described herein remainssubstantially fluid upon deposition. Alternatively, in other instances,the ink exhibits a phase change upon deposition and/or solidifies upondeposition. Moreover, in some cases, the temperature of the printingenvironment can be controlled so that the jetted droplets of inksolidify on contact with the receiving surface. In other embodiments,the jetted droplets of ink do not solidify on contact with the receivingsurface, remaining in a substantially fluid state. Additionally, in someinstances, after each layer is deposited, the deposited material isplanarized and cured with electromagnetic (e.g., UV) radiation prior tothe deposition of the next layer. Optionally, several layers can bedeposited before planarization and curing, or multiple layers can bedeposited and cured followed by one or more layers being deposited andthen planarized without curing. Planarization corrects the thickness ofone or more layers prior to curing the material by evening the dispensedmaterial to remove excess material and create a uniformly smooth exposedor flat up-facing surface on the support platform of the printer. Insome embodiments, planarization is accomplished with a wiper device,such as a roller, which may be counter-rotating in one or more printingdirections but not counter-rotating in one or more other printingdirections. In some cases, the wiper device comprises a roller and awiper that removes excess material from the roller. Further, in someinstances, the wiper device is heated. It should be noted that theconsistency of the jetted ink described herein prior to curing, in someembodiments, should desirably be sufficient to retain its shape and notbe subject to excessive viscous drag from the planarizer.

Moreover, a support material, when used, can be deposited in a mannerconsistent with that described hereinabove for the ink. The supportmaterial, for example, can be deposited according to the preselected CADparameters such that the support material is adjacent or continuous withone or more layers of the ink. Jetted droplets of the support material,in some embodiments, solidify or freeze on contact with the receivingsurface. In some cases, the deposited support material is also subjectedto planarization.

Layered deposition of the ink and support material can be repeated untilthe 3D article has been formed. In some embodiments, a method ofprinting a 3D article further comprises removing the support materialfrom the ink.

It is also possible to form a 3D article from an ink described hereinusing stereolithography (SLA), contacted SLA (cSLA), or digital lightprocessing (DLP) 3D printing. For example, in some cases, a method ofprinting a 3D article comprises retaining one or more inks describedherein in a fluid state in a container and selectively applying energyto the one or more inks in the container to solidify at least a portionof a fluid layer of the ink, thereby forming a solidified layer thatdefines a cross-section of the 3D article. Additionally, a methoddescribed herein can further comprise raising or lowering the solidifiedlayer of ink to provide a new or second fluid layer of unsolidified inkat the surface of the fluid ink in the container, followed by againselectively applying energy to the ink in the container to solidify atleast a portion of the new or second fluid layer of the ink to form asecond solidified layer that defines a second cross-section of the 3Darticle. Further, the first and second cross-sections of the 3D articlecan be bonded or adhered to one another in the z-direction (or builddirection corresponding to the direction of raising or lowering recitedabove) by the application of the energy for solidifying the ink.Moreover, selectively applying energy to the ink in the container cancomprise applying electromagnetic radiation, such as UV radiation orvisible radiation, having a sufficient energy to cure the ink. In someinstances, the UV light has an average wavelength of 320-380 nm, 340-370nm, or 350-360 nm. In some cases, the curing radiation is provided by acomputer controlled laser beam or a DLP light source or projector. Inaddition, in some instances, raising or lowering a solidified layer ofink is carried out using an elevator platform disposed in the containerof fluid ink. A method described herein can also comprise planarizing anew layer of fluid ink provided by raising or lowering an elevatorplatform. Such planarization can be carried out, in some cases, by awiper or roller.

It is further to be understood that the foregoing process can berepeated a desired number of times to provide the 3D article. Forexample, in some cases, this process can be repeated “n” number oftimes, wherein n can be up to about 100,000, up to about 50,000, up toabout 10,000, up to about 5000, up to about 1000, or up to about 500.Thus, in some embodiments, a method of printing a 3D article describedherein can comprise selectively applying energy to an ink in a containerto solidify at least a portion of an nth fluid layer of the ink, therebyforming an nth solidified layer that defines an nth cross-section of the3D article, raising or lowering the nth solidified layer of ink toprovide an (n+1)th layer of unsolidified ink at the surface of the fluidink in the container, selectively applying energy to the (n+1)th layerof ink in the container to solidify at least a portion of the (n+1)thlayer of the ink to form an (n+1)th solidified layer that defines an(n+1)th cross-section of the 3D article, raising or lowering the (n+1)thsolidified layer of ink to provide an (n+2)th layer of unsolidified inkat the surface of the fluid ink in the container, and continuing torepeat the foregoing steps to form the 3D article. Further, it is to beunderstood that one or more steps of a method described herein, such asa step of selectively applying energy to a layer of ink, can be carriedout according to an image of the 3D article in a computer-readableformat. General methods of 3D printing using stereolithography arefurther described, inter alia, in U.S. Pat. Nos. 5,904,889 and6,558,606.

Performing a printing process described above can provide a printed 3Darticle from an ink described herein that has a high feature resolution.The “feature resolution” of an article, for reference purposes herein,can be the smallest controllable physical feature size of the article.The feature resolution of an article can be described in terms of a unitof distance such as microns (μm), or in terms of dots per inch (dpi). Asunderstood by one of ordinary skill in the art, a higher featureresolution corresponds to a higher dpi value but a lower distance valuein μm. In some cases, an article formed by depositing or solidifying anink described herein can have a feature resolution of about 500 μm orless, about 200 μm or less, about 100 μm or less, or about 50 μm orless, including at elevated temperatures. In some embodiments, anarticle has a feature resolution between about 50 μm and about 500 μm,between about 50 μm and about 200 μm, between about 50 μm and about 100μm, or between about 100 μm and about 200 μm. Correspondingly, in someinstances, an article described herein has a feature resolution of atleast about 100 dpi, at least about 200 dpi, at least about 250 dpi, atleast about 400 dpi, or at least about 500 dpi. In some cases, thefeature resolution of an article is between about 100 dpi and about 600dpi, between about 100 dpi and about 250 dpi, or between about 200 dpiand about 600 dpi.

V. Printed 3D Articles

In another aspect, printed 3D articles are described herein. In someembodiments, a printed 3D article is formed from one or more inksdescribed herein. Any ink described hereinabove in Section I may beused. For example, in some cases, the 3D article is formed from a singleink described herein, such as an ink comprising a thiol monomer, an enemonomer, and an additional (meth)acrylate monomer differing from the enemonomer. Moreover, the thiol monomer and the ene monomer, when cured,can together form a poly(thiol-ene). Similarly, the additional(meth)acrylate monomer, when cured, can form a poly(meth)acrylate. Insome such cases, the poly(thiol-ene) and the poly(meth)acrylate togetherform an interpenetrating polymer network.

A printed 3D article described herein may also be formed from aplurality of differing inks. For instance, in some embodiments, aprinted 3D article is formed from a first ink and a second ink describedhereinabove in Section I. In some such cases, the first ink comprises athiol monomer and the second ink comprises an ene monomer. The firstand/or second ink may also comprise an additional (meth)acrylate monomerthat differs from the ene monomer. Additionally, as describedhereinabove, such an additional (meth)acrylate monomer of a first orsecond ink can form a polymer network (specifically, apoly(meth)acrylate network) that differs from the polymer network(specifically, the poly(thiol-ene)) formed by the thiol and enemonomers. Additionally, in some instances, the two polymer networkstogether form an interpenetrating polymer network.

Some embodiments described herein are further illustrated in thefollowing non-limiting example.

Example Ink for 3D Printing

An ink according to one embodiment described herein was prepared asfollows. First, 15-25 wt. % pentaerythritol tetra(3-mercaptopropionate)(PETMP), 10-50 wt. % oligomeric (meth)acrylate, and 20-50 wt. %monomeric (meth)acrylate, 1-4 wt. % photoinitiator, and 0.1-1 wt. %polymerization inhibitor were mixed and provided in a liquid state in amanner described hereinabove in Section I. Specifically, the individualcomponents of the ink were combined and mixed. The mixture was heated toa temperature of about 60-75° C. with stirring. The heating and stirringwere continued until the mixture attained a substantially homogenizedliquid state. The liquid mixture was then filtered to removeparticulates.

Following preparation of the ink, the ink was used to form various 3Darticles using a cSLA 3D printing system. The resulting articles werevery tough, flexible, and unbreakable under all conditions tested.

All patent documents referred to herein are incorporated by reference intheir entireties. Various embodiments of the invention have beendescribed in fulfillment of the various objectives of the invention. Itshould be recognized that these embodiments are merely illustrative ofthe principles of the present invention. Numerous modifications andadaptations thereof will be readily apparent to those skilled in the artwithout departing from the spirit and scope of the invention.

That which is claimed:
 1. An ink for use in a three-dimensional printingsystem comprising: up to 30 wt. % thiol monomer; and up to 90 wt. % ofat least one of an ene monomer and an ene oligomer, based on the totalweight of the ink.
 2. The ink of claim 1, further comprising 0.1-5 wt. %photoinitiator, based on the total weight of the ink.
 3. The ink ofclaim 1, wherein the thiol monomer comprises secondary thiol monomer. 4.The ink of claim 1, wherein the thiol monomer comprises pentaerythritoltetrakis(3-mercaptobutylate).
 5. The ink of claim 1, wherein the thiolmonomer comprises a plurality of differing thiol-containing species. 6.The ink of claim 1, further comprising a (meth)acrylate monomer thatdiffers from the at least one of an ene monomer and an ene oligomer. 7.The ink of claim 1, comprising up to 20 wt. % thiol monomer.
 8. The inkof claim 1, further comprising an inhibitor and/or a stabilizing agent.9. A kit for use in a three-dimensional printing system, the kitcomprising: a first ink comprising up to 30 wt. % thiol monomer, thethiol monomer comprising pentaerythritol tetrakis(3-mercaptobutylate);and a second ink comprising at least one of an ene monomer and an eneoligomer, the ene monomer or ene oligomer comprising a ethylenicallyunsaturated moiety; wherein the thiol monomer and the ene monomer arenot combined prior to printing.
 10. The kit of claim 9, wherein thesecond ink comprises a (meth)acrylate monomer that differs from the atleast one ene monomer and ene oligomer.
 11. The kit of claim 9, whereinthe first ink comprises a plurality of differing thiol-containingspecies.
 12. The kit of claim 9, wherein at least one of the first inkand the second ink comprise 0.1-5 wt. % photoinitiator, based on thetotal weight of the first ink and the second ink.
 13. The kit of claim9, wherein at least one of the first ink and the second ink comprise aninhibitor and/or a stabilizing agent.
 14. The kit of claim 9, whereinthe first ink comprises a plurality of thiol moieties.
 15. A printedthree-dimensional article formed from the ink of claim
 1. 16. A methodof printing a three-dimensional article comprising: Selectivelydepositing layers of an ink in a fluid state onto a substrate, whereinthe ink comprises the ink of claim
 1. 17. The method of claim 16,wherein the layers are deposited according to an image of thethree-dimensional article in a computer readable format.
 18. The methodof claim 16, wherein the ink comprises a (meth)acrylate monomerdiffering from the at least one ene monomer and ene oligomer, and themethod comprises further UV curing the (meth)acrylate monomer.
 19. Themethod of claim 16, wherein the thiol monomer comprises pentaerythritoltetrakis(3-mercaptobutylate).
 20. The method of claim 16, furthercomprising thermally curing the thiol monomer and the at least one enemonomer and ene oligomer.